This invention relates generally to a fuel injection system for internal combustion engines, and more particularly to a fuel injector for such a system operable normally under the urging of independent mechanical means.
A specific use of the present invention is with diesel engines. Operating on extremely heavy fuels and conventional diesel fuels, the power, efficiency, reliability and economical performance of diesel engines depend upon proper organization of the combustion process in the engine cylinders. One important component of this process is heavy fuel atomization by conventional, closed type of fuel injectors. The control of atomization is largely dependent upon the type of fuel pumps, fuel injectors, and combustion chamber configuration. However, the quality of the fuel utilized in internal combustion engines is not uniform, and the fuel injection equipment must be capable of operation with heavy fuel of poor quality as sometimes might be obtained. It is believed that the substantial majority of diesel engine malfunctions are initiated with an improper combustion process including primarily the failure of fuel pumps, fuel injectors and related equipment. This is accomplished because heavy fuels have unstable molecular structure as a result primarily of poor lubricant ability.
Heretofore, the closed type mechanical fuel injector having a fuel nozzle extending within a cylinder has utilized a spring loaded needle valve with a predetermined clearance and with the spring bias being adjustable for varying the loading on the needle valve. The mechanical components associated with such a fuel injector adversely affect the normal injection process when the components become worn or fatigued, as a result of the molecular structure of the heavy fuels. The vibration of internal parts and the wave effect in the high pressure fuel line from the fuel pump to the injector cause "secondary injection" which results in excessive emissions and carbon deposits on engine parts.
In the present design of the closed type fuel injectors, cavitation occurs very frequently. Existing fuel injection systems utilize different devices to prevent wave effect to avoid "secondary injection", but these systems require a drop in the fuel pressure to almost "zero" in the pressure line which causes cavitation in the fuel pressure lines and the associated fuel pump elements. At the same time it is very difficult to maintain accurate injection timing as viscosity of the fuels, hydraulic losses, elastic expansion of high pressure lines, etc. cause time delay of the fuel injection. All these effects create high exhaust temperatures, high emissions, excessive wear, and premature failure of major engine parts such as pistons, piston rings, valves, cylinder liners, and the like. It is very difficult to maintain identical injection pressures and patterns with a set of injectors using mechanical adjustment controls. It is practically impossible to maintain simultaneous injection timing on the engine with two or more injectors operated from one fuel pump as the injector springs do not have identical tension and the injector with the lesser spring tension opens earlier than the injector with a higher spring tension. Thus, as a result, the injection pattern is irregular and engine parts are often severely damaged. In addition, spring fatigue and needle valve wear have a substantial effect on the timing of injection processes when several injectors from one fuel pump are utilized.
Another major obstacle for proper organization of the combustion process with the closed type mechanical injectors is excessive fuel leakage between the needle valve and guide caused by excessive wear resulting from the poor quality of fuels oftentimes utilized. The lifting speed of the needle valve may be significantly decreased because the force between the spring and the differential pressure of fuel cannot increase fast enough for properly lifting the needle valve, and as a result the injection process is inadequate. Proper injection procedures require the camshaft cams to have a very sharp profile so the fuel pumps inject fuel very fast, but the injectors oftentimes do not react promptly. As a result, certain loads on the cams increase and associated contacting surfaces become fatigued or fractured resulting in engine malfunctioning.
Some hydraulic fuel injection systems heretofore have utilized a fluid control system operable under a predetermined pressure differential between the pressurized fuel and fluid control pressure directly acting on the needle valve. Examples of such prior art systems are shown in United States Pat. Nos. 3,416,506; 4,069,800; and 4,089,315. However, such fuel injection systems have not utilized the physical phenomenon known as a high fluid tension effect to provide a seal between a needle and associated guideway for significantly decreasing the clearance between the needle and guideway. On conventional, mechanically controlled fuel injectors clearances between the needle and guideway are comparatively large, such as 8 to 35 microns, in order to provide adequate free movement of the needle. However, such desirable fluid controlled fuel injection systems have not utilized a backup system in the event of a failure in the fluid control system, such as a rupture of a fluid control line, for example, and this creates a possible potential safety problem since an uninterrupted flow of fuel into the cylinder might occur from the pressurized fuel line.